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Climate Hustle

Is Antarctica losing or gaining ice?

What the science says...

Select a level... Basic Intermediate

Satellites measure Antarctica is gaining sea ice but losing land ice at an accelerating rate which has implications for sea level rise.

Climate Myth...

Antarctica is gaining ice
"[Ice] is expanding in much of Antarctica, contrary to the widespread public belief that global warming is melting the continental ice cap." (Greg Roberts, The Australian)

Update Nov. 7 2015

A study published by Jay Zwally and his team on Oct. 30 (Zwally et al. 2015) has suggested that until 2008 there might have been a bigger increase in ice on East Antarctica than there is a decrease in the west, meaning that total Antarctic land ice is increasing. While their results for the Antarctic Peninsula and much of West Antarctica agree with other research, the study disagrees with many other techniques. We will update this discussion once more studies address this issue. Until then here are links to some recently published takes on the study:

A controversial NASA study says Antarctica is gaining ice. Here’s why you should be skeptical - Chris Mooney (Nov. 5)

NASA Scientist Warned Deniers Would Distort His Antarctic Ice Study — That's Exactly What They Did - Media Matters (Nov.4)

More on Antarctic Ice Melt - ClimateCrocks (Nov. 3)

Is Antarctica Gaining or Losing Ice? Hint: Losing. - Phil Plait (Nov. 3)

Q&A: Is Antarctica gaining or losing ice? - Carbon Brief (Nov. 3)

Just Because Antarctica Might Be Gaining Ice Doesn't Mean Climate Change Isn't Happening - Vice (Nov. 2)

Skeptic arguments that Antarctica is gaining ice frequently hinge on an error of omission, namely ignoring the difference between land ice and sea ice.

In glaciology and particularly with respect to Antarctic ice, not all things are created equal. Let us consider the following differences. Antarctic land ice is the ice which has accumulated over thousands of years on the Antarctica landmass itself through snowfall. This land ice therefore is actually stored ocean water that once fell as precipitation. Sea ice in Antarctica is quite different as it is ice which forms in salt water primarily during the winter months. When land ice melts and flows into the oceans global sea levels rise on average; when sea ice melts sea levels do not change measurably.

In Antarctica, sea ice grows quite extensively during winter but nearly completely melts away during the summer (Figure 1). That is where the important difference between Antarctic and Arctic sea ice exists as much of the Arctic's sea ice lasts all the year round. During the winter months it increases and before decreasing during the summer months, but an ice cover does in fact remain in the North which includes quite a bit of ice from previous years (Figure 1). Essentially Arctic sea ice is more important for the earth's energy balance because when it increasingly melts, more sunlight is absorbed by the oceans whereas Antarctic sea ice normally melts each summer leaving the earth's energy balance largely unchanged.

Figure 1: Coverage of sea ice in both the Arctic (Top) and Antarctica (Bottom) for both summer minimums and winter maximums
Source: National Snow and Ice Data Center

One must also be careful how you interpret trends in Antarctic sea ice. Currently this ice is increasing overall and has been for years but is this the smoking gun against climate change? Not quite. Antarctic sea ice is gaining because of many different reasons but the most accepted recent explanations are listed below:

i) Ozone levels over Antarctica have dropped causing stratospheric cooling and increasing winds which lead to more areas of open water that can be frozen (Gillet 2003, Thompson 2002, Turner 2009).


ii) The Southern Ocean is freshening because of increased rain and snowfall as well as an increase in meltwater coming from the edges of Antarctica's land ice (Zhang 2007, Bintanga et al. 2013). Together, these change the composition of the different layers in the ocean there causing less mixing between warm and cold layers and thus less melted sea and coastal land ice.

All the sea ice talk aside, it is quite clear that really when it comes to Antarctic ice and sea levels, sea ice is not the most important thing to measure. In Antarctica, the largest and most important ice mass is the land ice of the West Antarctic and East Antarctic ice sheets.

Therefore, how is Antarctic land ice doing?

Shepherd et al. 2012
Figure 2: Estimates of total Antarctic land ice changes and approximate sea level contributions using a combination of different measurement techniques (Shepherd, 2012). Shaded areas represent the estimate uncertainty (1-sigma).

Estimates of recent changes in Antarctic land ice (Figure 2, bottom panel) show an increasing contribution to sea level with time, although not as fast a rate or acceleration as Greenland. Between 1992 and 2011, the Antarctic Ice Sheets overall lost 1350 giga-tonnes (Gt) or 1,350,000,000,000 tonnes into the oceans, at an average rate of 70 Gt per year (Gt/yr). Because a reduction in mass of 360 Gt/year represents an annual global-average sea level rise of 1 mm, these estimates equate to an increase in global-average sea levels by 0.19 mm/yr.

There is variation between regions within Antarctica (Figure 2, top panel), with the West Antarctic Ice Sheet and the Antarctic Peninsula Ice Sheet losing ice mass, and with an increasing rate. The East Antarctic Ice Sheet is growing slightly over this period but not enough to offset the other losses.  There are of course uncertainties in the estimation methods but independent data from multiple measurement techniques (explained here) all show the same thing, Antarctica is losing land ice as a whole, and these losses are accelerating quickly.

Basic rebuttal written by mattking

Update July 2015:

Here is the relevant lecture-video from Denial101x - Making Sense of Climate Science Denial


Last updated on 8 November 2015 by BaerbelW . View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

Further reading

Tamino compares and analyses the long term trends in sea ice data from the Northern and Southern Hemisphere in Sea Ice, North and South, Then and Now.


On 20 Jan 2012, we revised this article upon learning it referenced an incorrect quote. We apologize to Dr. Michaels and to our readers for the error.


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Comments 401 to 450 out of 463:

  1. bozzza

    Sea ice in the SH is not relevant because the ice pack there has land under it. Whereas in the NH, i.e. the Arctic, the ice pack has sea under it.

    An honest comparison between the NH and SH can only be made between the two ice packs in their entirety.

    The amount of sea ice in the SH is miniscule, one might even be able to say that it is statistically zero (but I am too lazy to do the math), when compared to the size of the actual ice pack in the SH.

    When the NH ice pack finally disappears, enough people will notice and we can then pass laws making those who peddled their anti-science BS liable for all the damages that their actions will have caused by introducing them to somethng called “accepting personal responsibility for their actions.”

    If the SH ice pack disappears, not only will we be nationalizing 100% of the assets of those who, or whose ancestors because the proceeds of crime are still the proceeds of crime, peddled their anti-science BS to pay all the damages that their actions will have caused: We will also be stringing them up from lampposts because if the SH ice pack disappears, we are in for a world of hurt and we will seriously want to hold us some modern Nuremberg Trials.

  2. A heat pump works by using a refrigerant but instead of the coils that radiate away the heat being outside, they are usually, in one form or another, inside.

    What you call an “ocean pump” is not in fact a pump, but is a current that is part of what some call the global thermohaline circulation. Just because someone calls it a pump does not meant that a coherent and/or valid comparison can be made between it and other pumps.

    A current BTW that might be in serious danger from AGW.

    Also, if I were to guess, which I am about to do, my response to your final question would be along the lines of: The reason that the NH, and it’s condition, is better known then the SH’s condition is because for the past few hundred years NH countries dominated the globe, which includes said SH countries, and no one who thought that they mattered really gave a rat’s ass about the SH or anything but their own self-proclaimed superiority and/or exceptionalism.

  3. Ok, thanks for the food for thought on pumps versus mis-nomers...

    As for the last paragraph are you saying it isn't certain that the N.H. is warmer than the S.H.?

  4. I think the other point is that summer sea ice extent is important because of its effect on albedo. Winter sea ice at either pole has little climate impact. Also relevent is the question of why is sea ice increasing/decreasing. Changing temperature in both atmosphere and ocean is important at one pole; changing winds pushing pack further out is important at the other.

  5. (of course I read all your comments..)

  6. Bozzza - We know a lot more about past seaice extent in NH than SH. We know temperatures at both  poles are warming in recent times. Remember that the paradox with SH ice is why it is increasing despite ocean warning. (see Fig 3 in intermediate tab).

  7. @ 404, the new scientist article was short and sweet. It talked about how cold water sank at the poles and this dragged warmer water from the equator to replace it. The way people explain things is worth noting...

    This sentence- "As there is no returning flow of warm water to the south, the warmer air is trapped in the north."- was perculiar to the NH apparently, however... and this is what I can't wrap my laughing gear around!

  8. Bozzza, do some reading up on the thermohaline circulation. It is driven by salinity as well as temperature and yes, it is not symmetric across hemispheres. No warm Gulf stream down here. Pretty tough for agriculture in SH below 50S whereas 50N is relatively temperate.

  9. Bozzza

    Your question was “why” is the above- the fact that the NH is warmer than the SH- not common knowledge?

    I answered as honestly as I can with the knowledge I have.

    To answer your revised question would first require validating the claim that the NH is in fact warmer than the SH. That is easier said than done.

    Are you talking about total heat energy present north of the equator versus total heat energy south of the equator; and over what time frame. Are you talking about averages, means, or maximums versus minimums? Does all the data exist for the heat in all of the oceans in both hemispheres?

    Then determining “why”, if it is true, it is not common knowledge would require an extensive analysis of all the educational systems, all the media channels, and people’s preferences and abilities when it comes finding and retaining said information. And probably a lot of other variables that I am not aware of.

  10. bozzza - Yes, the NH is warming faster than the SH:

    HadCRUT4 NH and SH


    This is wholly unsurprising - land warms (and cools) faster than ocean, and the SH has less land relative to ocean area (warming differential predicted by Svante Arhennius, 1896, p265). This is also partly due to Arctic amplification having an impact (shallow sea with ice surrounded by land) compared to the Antarctic (land ice surrounded by water)

    What is your point?

  11. @ 408, yeh just still haven't got my head around this thermohaline cycle yet but even more to the point I feel the basic information of the NH being warmer than the SH should be much more common knowledge than it is if we are to save the world basically... it just confuses me as to why it isn't a high priority piece of information...

  12. @ 410, did you say the Arctic Ocean is not deep?

    In trying to make sense of the whole shebang in mentally digestable chunks what effect would this have exactly?

  13. bozzza - Average depth of the Arctic Ocean is ~1000m, while globally oceans average ~3700m, while the Southern Ocean around Antarctica averaging 4000-5000m. 

  14. bozzza - The differences in the Arctic are perhaps 1/4 the ocean thermal mass as global ocean averages, small overall size (the smallest ocean), being almost surrounded by land (which warms faster), more limited liquid interchanges due to bottlenecking than the Antarctic, and very importantly considerable susceptibility to positive albedo feedbacks; as less summer ice is present given current trends, solar energy absorbed by the Arctic ocean goes up very rapidly. 

    Given the land/ocean balances alone, the northern pole should warm ~10% faster than the southern. 

    Regarding warm/cold water exchanges, as scaddenp recommended I suggest reading up on global thermohaline circulation.  

    Thermohaline circulation

    While these overall effects may not be intuitive, they are very well established. 

  15. There's an interesting time-series of models of ice thickness and other information here:

    There's only the last 5 years of thickness represented, but it would be interesting to see a specific date animated as a gif (as opposed to the changes over a year), particularly at minimum and maximum days?

  16. (Apologies, just realised with changing pages to create an account, I ended up posting on the Antarctic comment thread rather than the Arctic thread I was reading. However I can't see a delete comment button?)

  17. Everyone should be happy, more sea ice means less ocean level rising. FACT.

  18. Perhaps I'm dense, ghoward.  Could you explain further?  Could you also give a method that results in global net sea ice increase over a meaningful time period?

  19. Sea ice is frozen sea water. Can you explain the mechanism behind your assertion ghoward?

  20. "Because a reduction in mass of 360 Gt/year represents an annual global-average sea level rise of 1 mm, these estimates equate to an increase in global-average sea levels by 0.19 mm/yr."

    Is my math correct in interpreting this statement to mean that it will take five years to raise sea level 1 mm and 125 years to raise sea level 1 inch?  Is the 360 GT per year just from Antarctic land ice or global land ice>

  21. renbuild1,

    Your math would be correct if the rate of melt were not rising.  Since the rate of melt is measured to be increasing rapidly, it will take much less  than 125 years for 1 inch of melt.  Recent measurements in West Antarctic indicate that the ice sheet there has passed its tippiing point.  Dr. Ringot, an Antarctic and Greenland specialist and coauthor on Hansen's recent paper on sea level rise, claimed that their data indicated that the West Antarctic Ice Sheet alone would melt in decades to centuries with a sea level rise of at least 10 feet.  Decades to centuries is a large range, but 10 years ago the same scientists were saying thousands of years for the sheet to melt.  This melt increase will occur in a non linear manner.  How much risk are you willing to take that it will not be decades??  Obviously Dr. Ringot feels it is possible or he would not have coauthored Hansen's paper.  10 feet of sea level rise would wipe out all of south and east Florida.

    When processes are known to be increasing rapidly it is inappropriate to extrapolate past melt rates far into the future.  Many things are hard to predict, especially the future.

    The current rate of sea level rise from all sources is 3-3.5 mm/year.  It is increasing.  How much sea level rise is acceptable?  In Tampa, Florida, where I live, we just had a flood where many homes reportedly had 2-19 inches of water inside.  Since 9 inches of sea level rise has been measured in Florida, many of those homes would not have flooded without sea level rise.  How much did AGW contribute to the extraordinary rain?  At least some.  This is damage caused today by AGW.  It will only increase in the future.

  22. renbuild1 - Geometric and exponential growth rates are not our friend here. We have to take acceleration into account.

    Antarctic Ice Mass

    Antarctic ice mass trend

    [Source: see Fig. 10]

    Greenland ice mass


  23. Antarctic ice loss is certainly accelerating. A plot of the rate of change of mass balance from the data graphed below (two clicks down the link) perhaps is starting to show an increase in that acceleration,  LINK , although it is early days for anything more than speculation.

     Antarctic mass balance

  24. Antarctic sea ice extent has drastically changed it's trajectory over the last 2 weeks: is there any sensible explanation for this?

  25. bozzza @424,
    The Antarctic sea ice area anomaly has gone negative in the last couple of days, the first time that has happened in four years. Prior to that (back in 2011), the SIA wobbled its way positive and negative with a long-term trend upward of 15,000 sq km pa. Seeing this recent return to negative anomalies is a return to that level of trend. It is perhaps the deviation from that long-term trend that would be easier explained, easier than the return to it.

    This graph (usually 2 clicks to 'download your attachment') shows recent years of SIA up to January 2015 but doesn't really capture that long term trend. I will upload something that does when I have a moment.

  26. Antarctic SIA 1979-2015

  27. bozzza @424,

    For one theory see:,724.msg60178.html#msg60178

    I believe that the current downward fluctuation in Antarctic Sea Ice Extent if likely associated with the influence of our currently strong El Nino on the average location of the Amundsen Bellingshausen Sea Low.

  28. Cheers, Jim: I googled "Amundsen Bellingshausen Sea Low" and found one of the first articles, " Study shows acceleration in melting of Antarctic ice shelves" and found the below to be a most interesting paragraph...


    "While it is fair to say that we're seeing the ice shelves responding to climate change, we don't believe there is enough evidence to directly relate recent ice shelf losses specifically to changes in global temperature," Fricker said.

    Read more:
    Follow us: @smh on Twitter | sydneymorningherald on Facebook

    ..there seems to be conflict amongst the talking heads so many thanks for keeping the debate informative!

  29. @ 426: the trend line could actually be getting steeper right this minute, apparently, ...according to the information in the graph itself [Trend line(regression 1979-2011) = 0.015 p.a.] could it not?

  30. bozzza @428.

    Do note that ice shelves and sea ice are not the same thing. (And also this thread is properly about ice sheets which is something else again entirely.)

    bozzza @429.

    While it is possible to consider fitting an upward curve to the graph @426 in place of the linear trend, the cause of the increases in Antarctic SIA/SIE would be worth looking at first.

    Like the loss of ice from Antarctica, the increase of Antarctic SIA/SIE is the product of two competing trends. Parts of the ocean are increasingly icy but other parts are losing ice. Also a lot less is known prior to the arrival of good satellite data in 1979. Fan et al (2014) suggests that ice may have been on an earlier downward trend, shrinking markedly up to 1979, strains perhaps of long-term natural variation at work? While other, for instance recently Hansen et al (2015), see large levels of sea ice growth in Antarctica as a by-product of AGW, and perhaps a by-product we should be very worried about.

    So, while fitting anything is possible, a reasoned fitment would be preferable to one that simply suits the mood of the author. In that regard, the linear trend provides a simple gauge of the situation, nothing more.

  31. Recent study shows mass balance increasing.

    Worth mentioning in the OP as an update? Or wait for the study to become available?


    [JH] Link activated.

    Like many of the SkS Rebuttal articles, the OP is in need of update. The all-volunteer SkS author team has embarked on an intitiative to update the Rebuttals. 

  32.  "A new NASA study says that an increase in Antarctic snow accumulation that began 10,000 years ago is currently adding enough ice to the continent to outweigh the increased losses from its thinning glaciers.

    The research challenges the conclusions of other studies, including the Intergovernmental Panel on Climate Change’s (IPCC) 2013 report, which says that Antarctica is overall losing land ice."

    Does this make the myth true?


    [JH] Link activated. 

  33. barry @431 & peter @432.

    Be mindful that this is not the first time in which Zwally has proclaimed the ERS & ICESat data as showing a net rise in Antarctic ice. A workshop paper in 2012 (abstact & video with gap in coverage - here) also resulted in calls here at SkS for revision to this post (along with more forceful demands elsewhere by the likes of the Lord Protector of Wattsupia).

    This time round, the journal article is so hot-off-the-press it has yet to appear on-line so it's a little early to be getting all excited. Until the new finding is appraised, best we make do with Hanna et al (2013) which is a paper co-authered by Zwally. It broadly discusses work in-hand plus future developments before concluding:-

    "However, it is unlikely that these refinements will change the consensus picture emerging: while Antarctica as a whole is losing mass slowly (assessed to be contributing 0.2 mm yr-1 sea-level equivalent by IMBIE2), Greenland, the Antarctic Peninsula, and parts of West Antarctica are together losing mass at a moderate (~ 1 mm yr -1 sea-level equivalent) rate today (~70% of this mass loss is from Greenland) and rates for each are becoming increasingly negative." (my bold)

    Figure 1 from Hanna et al (2013) demonstrates this 'emergence'.


    Figure 1 caption. Summary of Antarctic and Greenland mass-rate estimates. In the studies published before 20122 (left) and in 2012 (right) each estimate of a temporally-averaged rate of mass change is represented by a box whose width indicates the time period studied, and whose height indicates the error estimate. Single-epoch (snapshot) estimates of mass balance are represented by vertical error bars when error estimates are available, and are otherwise represented by asterisks. 2012 studies comprise IMBIE combined estimates2 (solid lines), and estimates by Sasgen and others16,20 and King and others11 (dashed lines), Zwally and others19 (dot-dashed lines), Harig and Simons89 and Ewert and others90 (dotted lines).

    Note that it is not just a need to reconcile this most recent Zwally paper with the other methods employed to assess East Antarctic ice balance. Both the linked pages @431&432 quote Zwally pointing out that these ERS & ICESat data have to be also reconciled with SLR data.

    And my answer to peter's question "Would this Zwally paper make the myth true?"  that answer would be  - "No". ERS & ICESat data continue to provide some evidential support for the 'Antarctica not losing ice' position which remains strongly a myth when presented as unequivocal fact, and doubly so when the mythical Antarctica ice balance is then presented as some natural global thermometer. Indeed, does it even work as a thermometer for Antarctica?

  34. @ 431 & 432 (barry & peter),


    I read it a bit differently:

    Although the article states: 
    A new NASA study says that an increase in Antarctic snow accumulation that began 10,000 years ago is currently adding enough ice to the continent to outweigh the increased losses from its thinning glaciers.

    This should be put into context, as Zwally also says that within a couple of decades (should the current loss rate remain) the losses will catch up to the gainings: "If the losses of the Antarctic Peninsula and parts of West Antarctica continue to increase at the same rate they've been increasing for the last two decades, the losses will catch up with the long-term gain in East Antarctica in 20 or 30 years—I don't think there will be enough snowfall increase to offset these losses."

    Am I correct to assume (if this study is correct), that net ice gain would only occur if we reduce the curret rate of ice loss?

  35. Regarding MA Rodgers' response in 433...  "Be mindful that this is not the first time in which Zwally has proclaimed the ERS & ICESat data as showing a net rise in Antarctic ice."

    What happened with the previous claim?  Was it shown to be in error in the 2013 paper co-authored by Zwally?

  36. "Does this make the myth true?"

    Myth? It's a new study. It's a good information service that points out uncertainties and alternative opinion. Such opinion may be weighed honestly against other opinion. The results here are a minority view (along with previous Zwally paper). Would it be good to give a robust appraisal of the topic, or reject alternative views if they interfere with the messaging?

    Mod reply says SkS is updating old rebuttal posts. I like robust posts that include uncertainties, indicate alternative opinion and sum up honestly. I'm fairly confident that will happen.

    (Thanks for the reply, JH)


    [JH] You're welcome. 

    The issue of whether Anatartica is gaining or losing land ice is fairly complex and the all-volunteer author team is busy sorting through all of the recent research on this topic.

  37. As I understand it, the GRACE results from NASA measure differences in gravitational pull to determine the mass of ice while the Zwally study (also NASA run) measures the height of the ice/snow cover, estimates how much of that height is ice vs snow, and then computes the resulting ice mass.

    Is there evidence of significant error/uncertainty in the GRACE data? If not, wouldn't it be inherently more reliable than Zwally's method? Basically, Zwally's study gets to 'net ice gain' by making different assumptions about the amount of snow cover. Assume more snow and we're back to 'net ice loss'. Yet GRACE doesn't have that issue at all... it reacts to gravitational pull. Differences in ice/snow elevation would have a neglible impact on gravitational pull. Only the total mass would matter... so how could it be showing less gravitational pull if there were more mass?

  38. Recommended supplemental reading:

    Is Antarctica Gaining or Losing Ice? Hint: Losing., Phil Plait, Bad Astronomy, Slate, Nov 3, 2015

  39. From the dictionary for Myth:

    1. a person or thing having only an imaginary or unverifiable existence

    2. an unfounded or false notion

    With this new study and other earlier ones from Nasa, and even the continual record Antarctic sea ice extent lately, Myth isn't the right word for the statement "Antarctica is gaining ice". It's in fact got some fairly substantial factual backing.

  40. At this point Zwally et al is quite the outlier, both from GRACE data alone and from the collection of other Antarctic mass balance work. 

    • Zwally et al might be wrong (or rather, far more wrong than other estimates, outside error bounds), perhaps due to the a snow/ice compaction model that is rather different from what is generally used - a very small error there would throw off their computations. 
    • Zwally et al  might be completely right, indicating that their compaction model is correct and nobody elses is, calling into question all those other works along with GRACE calibrations. I consider this rather unlikely. 
    • Or Zwally et al might be off-base, but other studies are overestimating mass loss somewhat. 

    We're going to have to wait and see how the science progresses. At this point, however, most of the evidence indicates some mass loss from the Antarctic continent, Zwally et al is inconsistent with both the GRACE gravity data and estimates of the sea level rise budget, and we need to be careful not to fall prey to 'single-study syndrome'.

  41. The Zwally et al (2015) pdf.

  42. If Antarctica really has been gaining mass, we are in deeper doodoo than we knew, because sea level has been rising fast even without any contribution from Antarctica. As the years pass, Antarctica's lowering of sea level (by accumulating water as snow and ice) will decrease until eventually (20 years Zwally estimated) Antarctica will start to contribute to sea level rise. So I very much hope Zwally's new study turns out to be wrong.

  43. The wind patterns around Antarctica have been changing over long term observation: the fact that the southern hemisphere is colder than the northern is the start of all methodical theory regarding climate change.

    I can't believe Venus ever had water but if it did the science says our oceans will never boil away as there are too many negative feedbacks, the presence of Antarctica obviously being the main one!

  44. It is common to assume that the Earth's crust is solid.  It is not.  The NASA study released 10/30/2015 concludes that Antarctica has been gaining ice mass for over 10,000 years.  That mass of ice has pushed parts of the continent below sea level.  It follows that the mantle around Antarctica should be similarly pushed up.  This is all a dynamic process which has a long lag time.  In short, Antarctica could be gaining ice mass and still causing the oceans to rise.

    Venus is a very poor model for the Earth as also is Mars.  Venus has four times the amount of nitrogen as the Earth which indicates that it started with an atmosphere of at least four times that of Earth.  Even today, with an atmosphere of 96% CO2, the average temperature at an altitude of 55 km, which corresponds to 6 km on Earth, is only 27 degrees C (80.6F).  Venus also receives twice the radiation from the sun as the Earth.


    [PS] If read the papers, you will see that GIA is very much part of calculation (and a key uncertainty)

    Please be careful to ensure comments do not drift offtopic. Nothing further on mars/venus here please.

  45. dale38 @444, as I understand it, the study to which you refer (Zwally et al, 2015) estimates the bedrock under the East Antarctic Ice Sheet is sinking, whereas most other models and observations suggest that it is falling.

    As to sea level rise due to displacement of mantle, because rock is denser than ice, more water must be drawn from the sea to displace the mantle than the volume of the mantle displaced.  It follows that accumulation of ice must result in a fall in sea level, and vice versa.

  46. My understanding is that the Arctic air temperatures are warming faster than the Antarctic. We know that most of the anthropogenic CO2 is released in the northern hemisphere, according to this NASA model
    CO2 lasts in the air for hundreds of years, but mixing of air between NH and SH is rather slow. Is there an appreciable lag between CO2 levels in the NH and those in the SH, and if so is it enough to contribute to the difference in warming between the Arctic and Antarctic?

  47. Richard Lawson @446.

    There is a lag but it measures months and does little more than ensure the annual cycle is missing over Antarctica. There is a graph of a model & there are fancy videos of it if you look. The fanciest is this NOAA graphic but that is a bit too fancy so it is less good at showing the lag that it should be.

  48. Richard Lawson @446, MA Rodger is correct that the lag time between NH and SH is quite small, but I believe he understates it.  To properly appreciate it, here are the annual average CO2 concentrations for four stations posted by Ferdinand Engelbeen in a discussion at Climate Etc:

    Drawing a horizontal line at any level shows the South Pole Concentration to lag the Mauna Loa concentration by approximately 1.5 years.  The SH lag to the NH will be about the same, slightly less for the lag to the global average.  The model for the graph to which MA Rodger links uses a lag of 22 months for SH to NH.  As MA Rodger notes, that is too small a lag to result in appreciable forcing differences, and makes almost no contribution to the different temperature histories.

    The most probable explanation of the different temperature histories is geographical.  Specifically while the Arctic is sea level sea ice surrounded by land, the Antarctic is a very high altitude plateau of land ice surrounded by ocean.  These differences have the effect that:

    1)  The Antarctic climate is significantly isolated from the global climate by circumpolar winds and currents, actin as an insulating barrier against heat transfer to the Antarctic;

    2)  The high altitude of the Antarctic plateau keeps local weather conditions below freezing throughout the summer, limiting albedo changes in summer;

    3)  The ocean surrounding the Antarctic tends to melt any snowfall, limiting any albedo changes in winter (a factor partly offset by changes in the extent of sea ice).

    In contrast, in the Arctic, Atlantic and to a lesser extent Pacific waters are actively channelled into the Arctic, thereby connecting Arctic temperature responses to those in the NH tropics and mid-latitudes.  Arctic sea ice melts in summer to very high latitudes, and gains melt ponds and polynaya over its full extent.  The sub arctic snow in winter primarilly falls on land where it can remain in situ and have a major contribution to albedo effects.  The net effect is a much stronger albedo feedback in the NH than in the SH, enhance because the large land mass in the NH results in larger temperature fluctuations in any event.  

  49. Richard... There's also a really good animated graph from Carbon Tracker that shows the NH/SH trends in a really cool way. LINK

  50. MA, Tom and Rob, Many thanks for your helpful responses, particularly for the beautiful dance of CO2 levels in Rob's link.

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